g Tutorial Exercise Suppose that a large mixing tank initially holds 600 gallons of water in which 50 pounds of salt have been dissolved. Another brine solution is pumped into the tank at a rate of 3 gal/min, and when the solution is well stirred, it is then pumped out at a slower rate of 2 gal/min. If the concentration of the solution entering is 3 lb/gal, determine a differential equation for the amount of salt A(t) in the tank at time t > 0.